This invention relates to a high-voltage resistor unit and a high-voltage variable resistor unit, and more particularly to a high-voltage variable resistor unit called a focusing pack which is used for adjusting a focusing voltage, a screen voltage or the like in a cathode ray tube (CRT) or the like.
A high-voltage variable resistor unit which is a typical example of a high-voltage resistor unit is generally put to use while being mounted on a transformer casing of a fly-back transformer and is constructed so as to output at least one of a screen voltage and a focusing pack. There has been recently proposed a high-voltage variable resistor unit called a double-focusing type which is adapted to generate a plurality of focusing voltages and more specifically two kinds of focusing voltages. The conventional high-voltage variable resistor unit is generally classified into a type of generating only a focusing voltage, that of generating both a focusing voltage and a screen voltage, and the like. Such a conventional high-voltage variable resistor unit includes a capacitor called a dynamic focusing capacitor for cutting a DC component and that for a filter, which may be often connected in parallel between an output electrode for a focusing voltage and a ground electrode and between the output electrode and a signal input terminal. The high-voltage variable resistor unit is combined with a fly-back transformer, so that the capacitors are arranged on a rear surface side of a circuit board arranged in an insulating casing which is open at one end thereof. Such arrangement of the capacitors on the rear surface side of the circuit board causes a terminal fitment electrically connected to the output electrode for a focusing voltage for connection of a lead wire of each of the capacitors thereto to be likewise arranged on the rear surface side of the circuit board. In the prior art, the terminal fitment generally has a lead wire connected thereto for outputting the focusing voltage in addition to the lead wire of the capacitor, resulting in the focusing voltage being outputted.
In order to facilitate the connection, a structure is proposed wherein a terminal member including a contact section adapted to be electrically connected to an output electrode by only contacting with the output electrode and without soldering is arranged between a front surface of the circuit board and the insulating casing, resulting in a connection conductor being connected to the terminal member without soldering. Also, another structure is proposed which is so constructed that electrical connection to both the ground electrode and an input electrode is carried out by means of a terminal member and without soldering. In the prior art, a front surface section of the output electrode with which the contact section of the terminal member is contacted is covered with a resistive paint layer formed by printing while having a part of a resistive circuit pattern superposed thereon. Then, the contact section of the terminal member is contacted with the resistive paint layer.
The above-described construction wherein the contact section of the terminal member is contacted through the resistive paint layer with the output electrode causes a resistance of the resistive paint layer in a thickness direction thereof to exist between the output electrode and the contact section. However, a study by the inventors revealed that connection of the capacitor for cutting the DC component between the output electrode and the signal input terminal for the purpose of inputting a dynamic focusing signal of a parabolic shape to the signal input terminal often causes a current in a relatively large amount to flow through the output electrode and signal input terminal. Also, it was found that a current is caused to flow in a relatively large amount to other output electrodes and the ground electrode through the contact section of the terminal member.
In such an instance, an increase in resistance of the resistive paint layer in the thickness direction thereof causes an increase in current flowing between the contact terminal of the terminal member and the electrodes, leading to an increase in heat generation therefrom. The heat thus generated results in a variation in resistance of the high-voltage variable resistor unit, so that an output voltage thereof is varied.